Yes, I know this is Part 11, but this is all I can come up with so far, and it's been bizzing around in my head for MONTHS!

Thanks to Stevey711, inufan13, shortynme, ClassicalNadia, GWENxTRENT, and dragonrider for the replies!

Aang woke up in a cold sweat. It was the morning of his thirteenth birthday.
His stomach lurched at the thought of turning thirteen.
He walked out into te courtyard, sat on a bench, and sighed glumly.
Katara sat with him. "What's the matter, Aang? It's your birthday. あなた should be happy!"
"I - I really don't want to talk about it," he said.
"C'mon," Katara said. "I won't tell the world if it's a secret または something."
Aang gulped. "I..I have triskaidekaphobia," he admitted.
"Triskadekaphobia?" Katara asked. "I didn't know あなた were afraid of the number thirteen."
"It's bad enough I'm turning thirteen," Aang said. "It's also Friday the thirteenth!"
"Aang, you'll only get bad luck if あなた think あなた will," Katara told him.
"See, that's the problem!" Aang said. "How can I not think I'm going to get bad luck when it's my thirteenth birthday and Friday the thirteenth?"
"Aang," Katara said. "You're going to be fine. I'm sure of it."
"Really?" Aang asked her.
"Would I lie to you?" she asked in response.
"I guess not," Aang said.
Katara gave him a playful shove. Aang just laughed.
"I don't think I have triskaidekaphobia anymore," Aang said.
With that, they shared a dep, passionate kiss.
Goodbye, triskaidekaphobia, Aang thought happily.

I'll update again soon!